§ 17
How much flow does the pump give, and what size motor should it have?
Answer: When a hydraulic pump for a winch, a crane or a steering gear needs to be changed or faulted, you should be able to work out the flow from the pump's swept volume and rev count, and the power the motor should deliver at working pressure. If the flow in practice is far below what's calculated, the pump is worn.
Flow Q = Vg × n × ηv / 1.000 (l/min, Vg i cm³)
Hydraulisk effekt = p × Q / 600 (kW, p i bar, Q i l/min)
Motoreffekt = hydraulisk effekt / ηt
Moment T = Vg × p / (20π × ηmh), hvor den mekanisk-hydrauliske virkningsgrad ηmh = ηt / ηv
| Symbol | Meaning | Unit |
|---|---|---|
| vg | Pump's swept volume (nameplate) | cm³/omdr |
| n | Rotation speed | o/min |
| eta_v | Volumetric efficiency | % |
| p | Working pressure | bar |
| eta_t | Total efficiency | % |
| = | Flow from pump | l/min |
| = | Required motor power | kW |
| = | Hydraulic power in the oil | kW |
| = | Theoretical flow (without leakage) | l/min |
| = | Torque on pump shaft | Nm |
Does not apply when
The calculator's own default values inserted. The figures are calculated with exactly the formula the tool uses.
Substituted
Giver
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Når et hydraulisk spil eller en kran bliver langsom, eller når en pumpe skal skiftes, skal du kende det flow, pumpen bør give, og den motoreffekt, den kræver. Beregneren regner flow, moment og effekt ud fra pumpens slagvolumen, omdrejningstal og arbejdstryk.
Ankerspillets pumpe har 28 cm³/omdr og drives af en 4-polet elmotor på 1.500 o/min. Systemet kører 180 bar.
It means: Pumpen giver ca. 39.9 l/min, og motoren skal levere ca. 14.1 kW. Pumpeakslen skal have ca. 89.7 Nm.
Spillet er blevet langsomt. Du regner med, at den volumetriske virkningsgrad er faldet til 80 %.
It means: Flowet falder til 33.6 l/min mod 42 l/min teoretisk. Viser flowmåleren omtrent dette ved arbejdstryk, er pumpen slidt og skal skiftes.
Dækskranens pumpe har 71 cm³/omdr ved 1.800 o/min og 250 bar, med 95 % volumetrisk og 88 % total virkningsgrad.
It means: Pumpen leverer ca. 121.4 l/min, og motoren skal levere ca. 57.5 kW.
kW = bar × l/min / 600. 100 bar og 60 l/min er 10 kW i olien.
Dobbelt omdrejningstal giver dobbelt flow. Dobbelt tryk giver dobbelt effekt ved samme flow.